The present invention relates to devices for hemming elements of pressed sheet metal, for example motor vehicle body elements, of the known type comprising:
a fixed support structure, having a surface for supporting the sheet metal elements to be hemmed, PA1 a first hemming tool, for making a first bending of a peripheral edge of one of said sheet metal elements, said first hemming tool being rotatably supported by said fixed supporting structure around a first axis, and being movable between a rest position and a work position, PA1 a second hemming tool, for making a second bending of said peripheral edge following said first bending, in order to complete the hemming of said sheet metal elements, said second hemming tool being also supported by said fixed supporting structure so as to be movable between a rest position and a work position, and PA1 means for driving a cyclic movement of the first and second hemming tool between their rest positions and their work positions. PA1 a rotatable driving shaft rotatably mounted on said fixed support structure around a second axis which is parallel to and spaced apart from said first axis, PA1 first cam means mounted on said driving shaft and cooperating with first cam-following means associated with said first hemming tool, to drive the displacement of the first hemming tool from its rest position to its work position and then again to its rest position, in a first part of each round of rotation of the driving shaft, and to hold the first hemming tool in its rest position in a second part of each round of rotation of the driving shaft, PA1 second cam means mounted on said driving shaft, to drive displacement of said second hemming tool from its rest position to its work position and then again to its rest position, in said second part of each round of rotation of the driving shaft, and to hold the second hemming tool in its rest position in said first part of each round of rotation of the driving shaft, PA1 second cam-following means cooperating with said second cam means, PA1 an auxiliary supporting member carrying said second cam following means, which is rotatably mounted on said fixed support structure around said first axis, PA1 a supporting member for the second hemming tool, which is pivotable on said auxiliary supporting member around a third axis which is parallel to said first and second axes and said supporting member being also connected to the fixed support structure by means of a further articulated linkage member, PA1 third cam means carried by said driving shaft and cooperating with third cam following means carried by said supporting member of the second hemming tool, for further pushing the second hemming tool to its work position each time it is brought to said position by the second cam means.
Devices of the above indicated type have been used for a long time in the automotive industry, for example for hemming the sheet metal elements forming doors, engine hoods or rear doors of motor vehicles.
According to the conventional technique, said means for driving the movement of the two hemming tools are comprised of hydraulic cylinders. Recently however, the need has been felt for some applications of avoiding the use of hydraulic devices, resorting to lever transmission devices driven by an electric motor. A device of this type is for example known from International patent application WO-9305902.